In the integrated circuit industry, integrated circuits are manufactured on semiconductor wafers. These integrated circuits must be electrically probed in order to determine that the integrated circuits are functioning properly. In order to probe an integrated circuit, the wafer is placed into a test apparatus which contains a probe card. The probe card contains conductive needles which are used to make electrical contact to exposed conductive top portions of the integrated circuits. The top surface of the integrated circuits contains both dielectric and conductive materials. Through the course of testing, the probe needles are brought into contact with the dielectric and conductive material on the top surface. Portions of this dielectric and conductive material from the top surface of the wafer will adhere to the tips of the probe needles. As this dielectric and conductive residue coats the tip of the probe needles, the contact resistance of the test interconnections increases whereby yield can decrease and integrated circuit (IC) testing can become inconsistent over time.
In order to clean the residue off of the tips of the probe needles, several prior art techniques can be used. In a first form, the probe needles can be scraped against a stone burnishing pad. While the burnishing of the probe needles against a stone pad can reduce the amount of residue formed on the tip of the probe needles, this abrasive operation has several disadvantages. First, when using a burnishing operation, portions of the probe needle are actually ground away along with the residue, thereby reducing the effectiveness and life time of the probe needles. In addition, the burnishing operation does not result in uniform cleaning of all of the probe needles which are attached to the probe card. In addition, over time, the stone burnishing pad will eventually become coated with the residue which was removed from previously-cleaned probe needles. Once this residue on the stone burnishing pad becomes significant, the effectiveness of the stone burnishing pad for removing residue on probe needles is significantly reduced. In a worst case, when the stone burnishing pad is significantly coated with residue, the stone burnishing operation can actually place more residue on the probe needles rather than remove residue from the probe needles. Due to the down pressure and lateral motion required for burnishing operations, the probe needles can be mechanically damaged or misaligned by changing their position during the burnishing process.
In another form, the prior art can replace stone burnishing with a light sandpaper clean or a camel hair brushing operation. Both of these techniques also suffer from the same disadvantages previously discussed for stone burnishing.
In another form, a chemical clean, such as an alcohol clean or other solvent clean, can be used in an attempt to reduce residue on the probe card needles. In an alcohol clean, experimentation has shown that adequate probe needle cleaning is not achieved. Regarding any solvent clean, the solvent used to remove residue on probe needles could be destructive to the material used to mount the probe needles onto the probe card and destructive to the probe card material. Therefore, use of solvent cleans could inadvertently result in significant damage to the entire probe card assembly resulting in replacement of the probe card assembly. In addition, the solvent cleans are messy, and cannot be performed in situ with the wafer testing/probing process. Solvent and alcohol cleans suffer from a significant cycle time disadvantage and throughput disadvantage when compared to other alternatives.
Therefore, a need exists for an improved method for cleaning probe needles and like integrated circuit conductive contacts.